GB1422485A - Steering system for motor vehicles - Google Patents

Abstract

1422485 Power steering systems DEERE & CO 16 April 1974 [16 April 1973] 16580/74 Heading B7H A vehicle steering system includes hydrostatic steering gear 30 connected to a primary circuit, including a pump 10, sump 14 and valve unit 18, and to a secondary circuit, including a steering cylinder 82, the valve unit including a spool 22 with a throttling bore 46 communicating with a discharge bore 36, the spool being responsive to pressure created at the bore 46 to move from a first position, in which lands 60, 62 prevent flow from the pressure line 16, 20 to the steering gear 30 and return flow from the steering gear, to a second position in which such flows are allowed. The system includes a pressure reservoir 80 which opens into the valve by a line 78 and is connected between the working lines 84, 86 of the steering cylinder; line 78 connects with return sleeving line 32 via the bore 34 of the valve, hence leakage to sump via bore 36 and line 38 is prevented by land 64 until the pump 10 works at sufficient pressure to move the valve to the second position. Fluid delivered to the pressure line 16, 20 moves the spool to the second position to allow flow to, via bore 26 and line 28, and from, via lines 32, 38 and bores 34, 36, the steering gear. If an air/fluid mixture is delivered to bore 20 the pressure at the throttling bore drops and supply is cut off. Bore 36 contains an adjustable throttle and is connected to bore 26 by a pressure relief valve 32. A chamber 52 contains a spring 54 opposing the motion of the spool to the second position and communicates with the throttling bore via apertures 50 in a damping plate 48. In another embodiment (Figs. 4, 5, not shown) the system includes an auxiliary hydraulic load supply to which is controlled by the valve.